Motion simulator

ABSTRACT

A motion simulator is constructed from a base driving an intermediate member via a 6 DOF hexapod, and a platform driven by a 2DOF simulator is provided on the intermediate member to supplement pitch and roll.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/759,663 filed Jul. 8, 2015, which is the U.S. national phase ofInternational Application No. PCT/EP2013/067521 filed Aug. 23, 2013,which claims priority of British Application No. 1300552.5 filed Jan.14, 2013, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is concerned with a motion simulator. Morespecifically the present invention is concerned with a motion simulatorfor applications requiring a large excursion in at least one rotationaldegree of freedom.

BACKGROUND OF THE INVENTION

Motion simulators are well known in the art. The Stewart platform (orhexapod) is a well known form of simulator which moves a platformrelative to a base. Hexapods have six linear actuators arranged to movethe platform in six degrees of freedom (three linear, three rotational)relative to the base depending on which actuators are used incombination. The translational degrees of freedom are commonly known assurge (horizontal movement in the direction of travel), sway (horizontalmovement perpendicular to the direction of travel) and heave (verticalmotion). The rotational degrees of freedom are known as roll (rotationabout an axis parallel to the direction of travel), pitch (rotationabout a horizontal axis perpendicular to the direction of travel) andyaw (rotation about a vertical axis).

Hexapods have finite workspaces defined by the maximum and minimumexcursion of the platform, which in turn is defined by the limit oftravel of the actuators. For larger workspaces requiring furtherplatform movement in any given degree of freedom, it is known to providelonger hexapod actuators. Although this may achieve the desired result,it substantially increases the cost of the simulator (longer linearactuators are significantly more expensive than short ones), and cansometimes decrease its inherent stiffness. In some cases, hexapods aresimply unsuitable for the required degree of excursion.

Stiffness is an important property of the simulator, because itminimises undesirable vibration and oscillation of the platform, whichwould otherwise provide false accelerations, and forces on the subject.In known Stewart platforms there is therefore a trade off betweenmaximum platform excursion and stiffness.

There are various simulations which require a high excursion, or degreeof travel, in a specific rotational degree or degrees of freedom. Thiscan be used to simulate gravity or radial accelerations. For example,fuel tank testing, battery testing, fuel metering system testing,inertia measurements of equipment, testing instruments, fixation methodstesting, equipment containing/depending on liquids or magnets and anyequipment that requires an artificial horizon all require potentiallylarge platform movements in the global roll and pitch degrees offreedom. Providing a hexapod with long stroke actuators would providethe required functionality to a certain extent, but not in all cases.Large hexapods would also provide functionality which is notrequired—namely additional travel in the remaining four degrees offreedom.

As such, there is competing requirement to provide a stiff, compact andinexpensive simulator on the one hand, and to provide additionalmovement in the roll and pitch degrees of freedom on the other hand.

SUMMARY OF THE INVENTION

It is an aim of the present invention to overcome, or at least mitigatethis problem.

According to a first aspect of the invention there is provided a motionsimulator comprising:

a base and an intermediate member connected to the base by a hexapod,the hexapod being configured to move the intermediate member in sixglobal degrees of freedom relative to the base, the six global degreesof freedom including roll, pitch and yaw;

a platform connected to the intermediate member for movement in at leastone local rotational degree of freedom relative thereto;

a supplementary actuation assembly arranged to move the platformrelative to the intermediate member in the at least one local rotationaldegree of freedom, so as to supplement global movement of the platformin at least one of the global roll and pitch degrees of freedom.

Advantageously, the provision of a movable platform on an intermediatemember allows a greater range of movement of the platform. It will benoted that although the hexapod is a parallel manipulator (thusproviding the required stiffness), the intermediate member and platformare coupled in series (providing a high range of movement). In theembodiment discussed below, a 6 degree of freedom hexapod issupplemented by a 2 degree of freedom system constrained by a universaljoint.

Preferably, the platform and intermediate member are connected by ajoint is fixed to the intermediate member at a first side, and fixed tothe platform at a second side, which joint has degrees of freedom in thelocal pitch and roll axes of the intermediate member.

Preferably the supplementary actuation assembly comprises a firstsupplementary linear actuator mounted to the intermediate member at afirst end and to the platform at a second end. More preferably theplatform is connected to the intermediate member via a joint, and inwhich the first supplementary linear actuator is connected to theplatform at a position spaced from the joint so as to produce a momenton the platform. This results in a rotation of the platform using alinear actuator.

Preferably the joint is a universal joint, such as a cardan joint or aspherical joint. This allows rotation of the platform in two notionalhorizontal degrees of freedom of the intermediate member only. The term“universal joint” is used here to denote a joint having at least tworotational degrees of freedom. Preferably the platform is constrainedrelative to the intermediate member in all local degrees of freedomexcept roll and pitch.

Alternatively the joint may be a joint constrained in all but onerotational degree of freedom—i.e. a hinge joint.

Preferably the supplementary actuation assembly is a parallelmanipulator having at least two functionally parallel actuators. In thiscontext, “functionally parallel” means operating in parallel—i.e. bothbeing joined to the intermediate member and platform. This furtherenhances the stiffness of the overall manipulator. Preferably thehexapod and the supplementary actuation assembly overlap in threedimensional space. This provides a stiff, compact arrangement.Preferably the actuators are not parallel in a geometric sense—i.e. theyare at an oblique angle relative to each other.

The supplementary actuation assembly may comprise a second supplementarylinear actuator mounted to the intermediate member at a first end and tothe platform at a second end. Preferably the second ends of the firstand second actuators are spaced apart on the platform. Combinations ofmovement of the first and second actuators can thereby move the platformin the two degrees of freedom.

Preferably the hexapod is attached to the intermediate member at leastthree fixing points defining a first plane, and in which the first endor ends of the supplementary linear actuator or actuators are positionedon a first side of the first plane, opposite to the platform.

Preferably the hexapod is attached to the intermediate member at leastthree fixing points defining a first plane, and in which thesupplementary actuation assembly crosses the first plane. Morepreferably the at least three fixing points define a first surfacebounded by lines joining the at least three fixing points, and in whichthe supplementary actuation assembly crosses the first surface. Thisprovides a stiff, compact simulator.

Preferably the intermediate member comprises a central region and aplurality of legs, in which the hexapod is attached to the legs. Thisallows for a lightweight intermediate member with low inertia, and alsoallows the supplementary actuation assembly to pass between the legs tomake a more compact simulator. The legs may extend in the localhorizontal plane of the intermediate member.

Preferably the intermediate member comprises a leg extending into avolume defined by the hexapod, in which the supplementary actuationassembly is attached to the leg. By “volume defined by the hexapod” wemean a notional three dimensional space bounded by the hexapodactuators. Such a volume is bounded by surfaces extending the shortestpossible distance between adjacent actuators, and by a top surfacejoining the three areas where pairs of actuators are attached to theintermediate member.

Preferably the supplementary actuation assembly is attached to the legat a foot, the foot defined at an end distal to the platform.

Preferably the supplementary actuation assembly is configured to actuatethe platform relative to the intermediate member about two notionalhorizontal axes in the local coordinate system of the intermediatemember.

Preferably the hexapod comprises a plurality of linear actuators, inwhich the supplementary actuation assembly comprises at least one linearactuator having an excursion less than any of the linear actuators ofthe hexapod. In other words, instead of the prior art approach ofproviding six longer actuators in the hexapod, six “normal” lengthactuators are supplemented by two further actuators. Provision of 8normal-length actuators instead of 6 longer actuators is both lessexpensive and stiffer.

Preferably at least one of the hexapod and supplementary actuationassembly comprises at least one linear actuator, the at least one linearactuator comprising an electric motor driving a ball screw to advance apiston.

With parenthetical reference to the corresponding parts, portions orsurfaces of the disclosed embodiment, merely for purposes ofillustration and not by way of limitation, a motion simulator (100) isprovided comprising: a base (102); a platform (104, 106); and at leasteight linear actuators (150, 152, 154, 156, 158, 160, 176, 178) throughwhich the platform is connected to the base; wherein the at least eightlinear actuators are controllable to move the platform relative to thebase in at least six degrees of freedom.

The at least eight linear actuators may consist of exactly eight linearactuators (150, 152, 154, 156, 158, 160, 176, 178). Each of the eightlinear actuators may comprises an electric motor (170). Each of theeight linear actuators may be connected to the base via a universaljoint (162) and may be connected to the platform via a universal joint(164). The platform may comprise a first portion (104) and a secondportion (106). The first portion of the platform may be connected to thesecond portion of the platform via a universal joint (110).

In another aspect, a method of assembling a motion simulator is providedcomprising the steps of: installing a base on a surface that isimmovable in use; suspending a platform above the base; connecting afirst linear actuator between the base and the platform; connecting asecond linear actuator between the base and the platform; connecting athird linear actuator between the base and the platform; connecting afourth linear actuator between the base and the platform; connecting afifth linear actuator between the base and the platform; connecting asixth linear actuator between the base and the platform; connecting aseventh linear actuator between the base and the platform; andconnecting an eighth linear actuator between the base and the platform.

The method of assembly may comprise the steps of: connecting a universaljoint between the base and the first linear actuator; connecting auniversal joint between the base and the second linear actuator;connecting a universal joint between the base and the third linearactuator; connecting a universal joint between the base and the fourthlinear actuator; connecting a universal joint between the base and thefifth linear actuator; connecting a universal joint between the base andthe sixth linear actuator; connecting a universal joint between the baseand the seventh linear actuator; and connecting a universal jointbetween the base and the eighth linear actuator. The method of assemblymay comprise the steps of: connecting a universal joint between theplatform and the first linear actuator; connecting a universal jointbetween the platform and the second linear actuator; connecting auniversal joint between the platform and the third linear actuator;connecting a universal joint between the platform and the fourth linearactuator; connecting a universal joint between the platform and thefifth linear actuator; connecting a universal joint between the platformand the sixth linear actuator; connecting a universal joint between theplatform and the seventh linear actuator; and connecting a universaljoint between the platform and the eighth linear actuator. The platformmay comprise a first portion and a second portion and the method ofassembly may comprise the step of connecting a universal joint betweenthe first portion of the platform and the second portion of theplatform.

BRIEF DESCRIPTION OF THE DRAWING VIEWS

An example motion simulator according to the present invention will nowbe described by way of example with reference to the accompanyingfigures in which:

FIG. 1 is a perspective view of a motion simulator in accordance withthe present invention;

FIG. 2 is a plan view of the motion simulator of FIG. 1;

FIG. 3 is a front view of the motion simulator of FIG. 1;

FIG. 4 is a side view of the motion simulator of FIG. 1;

FIG. 5 is a perspective view of a part of the motion simulator of FIG.1;

FIG. 6 is a first perspective view of a sub-assembly of the motionsimulator of FIG. 1;

FIG. 7 is a further perspective view of a sub-assembly of a motionsimulator of FIG. 1; and

FIG. 8 is a perspective view of the motion simulator of FIG. 1 in anactuated state.

DETAILED DESCRIPTION OF THE INVENTION

Turning to FIG. 1, a motion simulator 100 generally comprises a base102, an intermediate member 104, and a platform 106. The intermediatemember 104 and the base 102 are joined and driven by a hexapod 108 andthe platform 106 and the intermediate member 104 are joined by a jointassembly 110 and driven by supplementary actuation assembly 112.

The base 102 is generally triangular in shape having a first, second andthird vertex 114, 116, 118 respectively, as shown in FIG. 2. The base102 is attached to a solid immoveable surface such as the floor of aworkshop by a known method. The base is positioned to globally immovableglobal axes XG, YG and ZG. Rotation about XG is roll, and rotation aboutYG is pitch. Rotation about ZG is yaw.

The intermediate member 104 is shown in more detail in FIGS. 6 and 7.The intermediate member 104 comprises three arms 120, 122, 124respectively, extending radially from a central region 126. Theintermediate member 104 has a notional local co-ordinate system havingaxes XL, YL and ZL, which is slightly vertically offset from the top ofthe central region 126. The local coordinate system moves with theintermediate member 104. In the neutral position shown in FIG. 1, ZG andZL are aligned, XG and XL are parallel, and YG and YL are parallel.

Each of the arms 120, 122, 124 are equally spaced about the localvertical axis ZL. Extending from the central region 126, parallel to andalong the local vertical axis ZL, there is provided a leg 128. The legis tubular and cylindrical and terminates in a foot 130 at an endopposite to the arms 120, 122, 124 and central region 126. The foot 130is in the form of a radially extending flange.

Extending in the 90 degree corner defined between the leg 128 and eachindividual arm 120, 122, 124, there is provided a web 132, 134, 136respectively which acts to stiffen the intermediate member 104.

The platform 106 comprises a plate member 138 which has a generally flatsupport surface 140. The platform 106 defines a support 142 extendingfrom the plate member 138 opposite to the support surface 140. Thesupport 142 is a generally solid, cylindrical member. The support 142terminates in a platform joint flange 144. A plurality of webs 146extend between the platform joint flange 144, support 142, and theunderside of the member 138 opposite the support surface 140.

The hexapod 108 comprises six linear actuators 150 to 160 respectively.Each of the linear actuators is substantially identical and, as such,only the actuator 150 will be described here, with reference to FIG. 5.The linear actuator 150 comprises a first universal joint 162 and asecond universal joint 164. Universal joints 162, 164 are at oppositeends of the actuator 150. Intermediate the universal joints 162, 164,there is provided a cylinder 166 which houses a piston 168 (shown moreclearly with respect to the third linear actuator 154 in FIG. 8). Thepiston 168 is mounted inside the cylinder 166 with a ball screw which isactuable via an electric motor 170 connected to the linear actuator 150proximate the first universal joint 162. A belt drive 172 connects themotor 170 to the ball screw such that the piston 168 can be driven inand out of the cylinder 166 by the motor 170.

The joint assembly 110 comprises a universal joint 174 in the form of acardan joint positioned on the local axis ZL and actuable about thelocal horizontal axes XL and YL.

Referring to FIG. 8, the supplementary actuation assembly 112 comprisesa first supplementary linear actuator 176 and a second supplementarylinear actuator 178. The supplementary actuators 176, 178 are similar tothe linear actuators 150 to 160 with the exception that they aregenerally shorter and have less travel; that is a lower range of motionfrom their compact state as shown in FIG. 5, to their extended state asshown, for example, in FIG. 8.

The motion simulator 100 is assembled as follows.

The base 102 is installed on a stationary, horizontal, flat surface suchthat it is immoveable in use. The intermediate member 104 is thensuspended above the base 102 via the hexapod 108.

The actuators of the hexapod 108 are arranged as follows.

Firstly, the platform 106 is oriented such that each of the arms 120,122, 124 is interspersed between two of the vertices 114, 116, 118 ofthe base 102 when viewed from above (see FIG. 2). The first actuator 150then extends diagonally from the first vertex 114 to the end of thefirst arm 120. The second linear actuator 152 extends from the secondvertex 116 to the first end of the first arm 120. The third linearactuator 154 extends from the second vertex 116 to the end of the secondarm 122, and the fourth linear actuator 156 extends from the thirdvertex 118 to the end of the second arm 112. The fifth linear actuator158 extends from the third vertex 118 to the end of the third arm 124and finally, the sixth linear actuator 160 extends from the first vertex114 to the end of the third arm 124. In this manner a hexapod or Stewartplatform is formed. It will be noted that the volume formed by thehexapod defined by the linear actuators 150 to 160 is penetrated by thedownwardly depending leg 128 of the intermediate member 104.

The platform 106 is then attached to the central region 126 of theintermediate member 104 via the joint assembly 110 for rotation aboutlocal axes XL and YL. The supplementary actuation assembly 112 is theninstalled in which the first supplementary linear actuator 176 extendsfrom the foot 130 of the intermediate member 104 between the first andsecond arms 120, 122 of the intermediate member 104 to a corner of theplate member 138 of platform 106. Similarly, the second supplementarylinear actuator 178 extends from the foot 130 of the intermediate member104 between the second and third arms 122 and 124 of the intermediatemember 104 to an adjacent corner of the plate member 138 of the platform106.

The first and second supplementary actuators 176, 178 are at amid-travel point when the platform 104 is horizontal. Retraction of thefirst supplementary actuator 176 and lengthening of the secondsupplementary actuator 178 rotates the platform 104 about local axis XL,and simultaneous lengthening or shortening of both supplementaryactuators 176, 178 rotates the platform 104 about joint axis YL.

Roll of the intermediate member 104 about the axis XG via the hexapod,and roll of the platform 106 about the local axis XL relative to theintermediate member, is shown in FIG. 8. It will be noted that a largeroll of the platform 106 about the global axis XG is achieved.

Variations fall within the scope of the present invention.

The free ends of the legs of the intermediate member 104 may be joinedby a peripheral structure (which may be circular—i.e. a ring- or anyother shape) which bounds the intermediate member.

In an alternative embodiment, motion of the universal joint 174 aboutthe local horizontal axes XL and YL may be performed by a pair of motorswith rotary output shafts directly driving the joint.

1.-19. (canceled)
 20. A motion simulator comprising: a base; a platform;and at least eight linear actuators through which the platform isconnected to the base; wherein the at least eight linear actuators arecontrollable to move the platform relative to the base in at least sixdegrees of freedom.
 21. The motion simulator according to claim 20,wherein the at least eight linear actuators consist of exactly eightlinear actuators.
 22. The motion simulator according to claim 20,wherein each of the eight linear actuators comprises an electric motor.23. The motion simulator according to claim 20, wherein each of theeight linear actuators is connected to the base via a universal jointand is connected to the platform via a universal joint.
 24. The motionsimulator according to claim 20, wherein the platform comprises a firstportion and a second portion.
 25. The motion simulator according toclaim 24, wherein the first portion of the platform is connected to thesecond portion of the platform via a universal joint.
 26. A method ofassembling a motion simulator comprising the steps of: installing a baseon a surface that is immovable in use; suspending a platform above thebase; connecting a first linear actuator between the base and theplatform; connecting a second linear actuator between the base and theplatform; connecting a third linear actuator between the base and theplatform; connecting a fourth linear actuator between the base and theplatform; connecting a fifth linear actuator between the base and theplatform; connecting a sixth linear actuator between the base and theplatform; connecting a seventh linear actuator between the base and theplatform; and connecting an eighth linear actuator between the base andthe platform.
 27. The method of assembling a motion simulator accordingto claim 26, comprising the steps of: connecting a universal jointbetween the base and the first linear actuator; connecting a universaljoint between the base and the second linear actuator; connecting auniversal joint between the base and the third linear actuator;connecting a universal joint between the base and the fourth linearactuator; connecting a universal joint between the base and the fifthlinear actuator; connecting a universal joint between the base and thesixth linear actuator; connecting a universal joint between the base andthe seventh linear actuator; and connecting a universal joint betweenthe base and the eighth linear actuator.
 28. The method of assembling amotion simulator according to claim 27, comprising the steps of:connecting a universal joint between the platform and the first linearactuator; connecting a universal joint between the platform and thesecond linear actuator; connecting a universal joint between theplatform and the third linear actuator; connecting a universal jointbetween the platform and the fourth linear actuator; connecting auniversal joint between the platform and the fifth linear actuator;connecting a universal joint between the platform and the sixth linearactuator; connecting a universal joint between the platform and theseventh linear actuator; and connecting a universal joint between theplatform and the eighth linear actuator.
 29. The method of assembling amotion simulator according to claim 26, wherein the platform comprises afirst portion and a second portion and comprising the step of connectinga universal joint between the first portion of the platform and thesecond portion of the platform.
 30. A method of controlling a motionsimulator having a base, a platform, and at least eight linear actuatorsthrough which the platform is connected to the base, comprising the stepof controlling the eight actuators to move the platform relative to thebase in at least six degrees of freedom.